For more than half a century, the cathode ray tube (CRT) has been the principal electronic device for displaying visual information. The widespread usage of the CRT may be ascribed to the remarkable quality of the display characteristics in the realms of color, brightness, contrast and resolution. One major feature of the CRT permitting these qualifies to be realized is the use of a luminescent phosphor coating on a transparent faceplate.
Conventional CRT's, however, have the disadvantage that they require significant physical depth, i.e. , space behind the actual display surface, making them bulky and cumbersome. They are fragile and, due in part to their large vacuum volume, can be dangerous if broken. Furthermore, these devices consume significant amounts of power.
The advent of portable computers has created intense demand for displays which are lightweight, compact and power efficient. Since the space available for the display function of these devices precludes the use of a conventional CRT, there has been significant interest in efforts to provide satisfactory so-called "flat panel displays" or "quasi flat panel displays," having comparable or even superior display characteristics, e.g. , brightness, resolution, versatility in display, power consumption, etc. These efforts, while producing flat panel displays that are useful for some applications, have not produced a display that can compare to a conventional CRT.
Currently, liquid crystal displays are used almost universally for laptop and notebook computers. In comparison to a CRT, these displays provide poor contrast, only a limited range of viewing angles is possible, and, in color versions, they consume power at rates which are incompatible with extended battery operation. In addition, color screens tend to be far more costly than CRT's of equal screen size.
As a result of the drawbacks of liquid crystal display technology, thin film field emission display technology has been receiving increasing attention by industry. Flat panel displays utilizing such technology employ a matrix-addressable array of pointed, thin-film, cold field emission cathodes in combination with an anode comprising a phosphor-luminescent screen. The phenomenon of field emission was discovered in the 1950's, and extensive research by many individuals, such as Charles A. Spindt of SRI International, has improved the technology to the extent that its prospects for use in the manufacture of inexpensive, low-power, high-resolution, high-contrast, full-color flat displays appear to be promising.
Advances in field emission display technology are disclosed in U.S. Pat. No. 3,755,704, "Field Emission Cathode Structures and Devices Utilizing Such Structures," issued 28 Aug. 1973, to C. A. Spindt et al.; U.S. Pat. No. 4,940,916, "Electron Source with Micropoint Emissive Cathodes and Display Means by Cathodoluminescence Excited by Field Emission Using Said Source," issued 10 Jul. 1990 to Michel Borel et al.; U.S. Pat. No. 5,194,780, "Electron Source with Microtip Emissive Cathodes," issued 16 Mar. 1993 to Robert Meyer; and U.S. Pat. No. 5,225,820, "Microtip Trichromatic Fluorescent Screen," issued 6 Jul. 1993, to Jean-Fr ed eric Clerc. These patents are incorporated by reference into the present application.
In flat panel displays of the field emission type, the electron emitting surface of the emitter plate and the opposed display face of the anode plate are spaced from one another at a relatively small but uniform distance over the full extent of the display. This spacing, typically on the order of 200 .mu.meters (microns), is large enough to prevent electrical breakdown between these two surfaces, and yet is small enough to assure that the desired thinness, high resolution and color purity are achieved. In a field emission display, this space is evacuated, typically to a pressure of approximately 10.sup.-7 torr.
One of the assembly problems associated with the fabrication of field emission flat panel displays relates to the method of providing electrical interconnects between the two plates comprising the display unit. In most cases, the great majority of the display electronics is included on one plate, typically the emitter plate, in order to minimize the number of interconnections between plates. With this example, however, in order to provide the anode voltage, there must be at least one electrical path from the emitter plate to the anode plate. In the case of the arrangement disclosed in the Clerc patent, there must be at least three inter-plate interconnections. One intuitive method of providing these interconnects might be to fabricate electrical paths through the substrate materials comprising the anode and emitter plates, and connect leads between bond pads on the external surfaces of the two plates after the plates are assembled. Another method, disclosed in European Patent Application No. 92301832.3, published 2 Sep. 1992, passes interconnect leads under and around the outside of the sealing material which forms the vacuum seal between the plates. Both of these methods undermine the integrity of the vacuum seal, and both add a level of complexity to the final assembly of the fiat panel display unit.
In view of the above, it is clear that there exists a need for an interconnect structure and a method for providing electrical interconnects between the emitter plate and the anode plate of a flat panel display which ensure vacuum integrity and which permit assembly of these plates employing less complex fabrication processes than are currently used.